Method for increasing the thermostability of organopolysiloxanes

ABSTRACT

A method of increasing the thermostability of organopolysiloxanes and compositions containing the same comprising introducing into organopolysiloxanes and compositions based on them 0.01 to 10 weight parts of a polyethynylpyridine or synergistic mixtures of 0.01 to 10 weight parts of a polyethynylpyridine with 1 to 10 weight parts of metal salts or an oxide of a metal per 100 weight parts of organopolysiloxane. The resulting thermostable organopolysiloxanes and compositions based on them find application in aviation, ship building industry, rocketry, and in other branches of the industry.

United States Patent [191 Berlin et a]. I

[ METHOD FOR INCREASING THE THERMOSTABILITY OF ORGANOPOLYSILOXANES [76] Inventors: Alfred Anisimovich Berlin, Leninsky prospekt, 57, kv. 9; Roza Mikhailovna Aseeva, l ulitsa Stroitelei, 7, korpus l, kv. 133; Semen Markovich Mezhikovsky, Raketny bulvar, l3, korpus 2, kv. 62; Alla Ilinichna Sherle, ulitsa Petrovka, 23/10, kv. 46-a; Nadezhda Alexeevna Tsepalova, ulitsa Garibaldi, l9, korpus 4, kv. 8; Evgeny Alexandrovich Goldovsky, ulitsa Udaltsova, l0, kv. 107; Tatiana Vladimirovna Zelenetskaya, ulitsa Fersmana, 7, kv. 49; Rozalia Komalovna Fatkulina, ulitsa Osipenko, 44, kv. 6; Alexandr Samoilovich Kuzminsky, Frunzenskaya naberezhnaya, 38, kv. 91, all of Moscow, USSR.

[22] Filed: Apr. 9, 1973 [21] Appl. No.: 349,082

Related US. Application Data [63] Continuation of Ser. No. 116,612, Feb. 18, 1971,

abandoned.

[52] US. Cl 260/827; 260/45.75 R; 260/458 N; 260/465 G; 260/465 UA; 260/883 R [51] Int. Cl. C08L 39/04; C08L 83/06 [4 Dec. 23, 1975 [58] Field of Search... 260/827, 824, 88.3 R, 45.8 N

[56] References Cited UNITED STATES PATENTS 2,224,944 12/1940 Young 260/45.8 N 3,061,565 10/1962 Collings 260/45.75 3,082,181 3/1963 Brown et a1. 260/45.75 3,098,836 7/1963 Bobear 260/45.75 3,137,670 6/1964 Maneri Z60/45.75 3,142,655 7/1964 Bobear 260/45.75 3,177,177 4/1965 Bobear 260/45.75

FOREIGN PATENTS 0R APPLICATIONS 540,127 10/1941 United Kingdom 260/883 R Primary Examiner-Wilbert J. Briggs, Sr. Attorney, Agent, or Firm-l-lolman & Stern [57] ABSTRACT 9 Claims, No Drawings industries and in other industries.

METHOD FOR INCREASING THE THERMOSTABILITY OF ORGANOPOLYSILOXANES Known in the art are method for increasing the. thermostability of polyorganosiloxanes by. introducing various stabilizing additives thereinto (such as iron oxide,

titanium dioxide, oxides-of cobalt, copper, manganese, nickel, salts of iron, amides, certain phosphates dialkylsebactes, etc.). 1 a I Thus, a method is known for increasing the thermostability of polyorganosiloxanes, residing in that introduced. into polyorganosiloxanes are such stabilizing additives as Cu 0, CuO; Cr O MnO qNi O or hydroxides of yttrium, zirconium, etc; in an amount of 0.001 to 8 parts by weight per 100 parts by weight of the polyorganosiloxanes.

The testing of the stabilizing effect shows that relative elongation at rupture of a test sample (a polyorganosiloxane composition without a stabilizer) is 23% after 7 days of ageing at a temperature of 250C, while 1 The organopolysiloxanes employed in the present invention are conventional andwell-known in the art.

of a polyethynylpyridine, or a mixture of a polyethynylpyridine with a metalliferous component. Polyethynylmethyl-5-ethynylpyridine,

in the case of a composition with Cu O as a stabilizing initial weight, while the stabilized polymer loses only 13% of its initial weight. Another known method for increasing the thermostability of polyorganosiloxanes envisages the use of 0.05 105 weight percent of amides as a stabilizing additive. Whentested for determining its physico-mechanical properties after ageing during 48 hours at a temperature of 300C, the reference sample (without a stabilizer) becomes destroyed, while that stabilized with 0.4 weight percent of diphenyl urea preserves 40% of its initial strength and shows 50% relative elongation (Federal Republic ofGermany Pat. No. 1,1 10,410; Czechoslovakian Pat. No. 99,408; US. Pat. No. 2,495,838).

Said methods are disadvantageous in that theydo not ensure adequate thermostability of stabilized polyorganosiloxanes at high temperatures.

The use of the above-mentioned stabilizers cannot prevent all those processes which may be lead to the destruction of polyorganosiloxanes at a temperature of 300C, while at a temperature above 300C the stabiliz- I ing effect is essentially lost altogetherQ pyridines may be produced by polymerizing corre sponding monomers'QSynthesis and some properties of polyethynylpyridines are described in the following studies; as, .l. Okamoto, D. Alia, Chem. and lndustry, 1964, 131 l; A. A. Berlin, 0'. B. Belova, 'A. l Sherle, N. A. Markova, High-molecular compounds, Chimica lndustria Acta, No.1, 172 (1969). i It is preferable that polyethynylpyridines should be introduced into polyorganosiloxanes in an amount of 0.01 to l0 parts by weight per 100 parts by weight of the polyorganosiloxanes.

As polyethynylpyridines it is preferable to use poly2- poly-4-ethynylpyridine, poly-2-ethynylpyridine.

The Applicants have detected the synergistic effect when using mixtures of polyethynylpyridines with metalliferous compounds that are selected from the group .consisting of metal salts, such as cerium naphthenate,

lanthanum naphthenate, ytterbium naphthenate,- or the oxides of metals such as copper oxide, barium oxide, aluminum oxide, cerium oxide, and iron oxide.

The mixture of polyethynylpyridines with a metalliferous component to be introduced should preferably be composed of 0.01 to 10 weight parts of a polyethynylpyridine and l to 10 weight'parts of a metalliferous component per 100 weight parts of polyorganosiloxanes. I

As a metalliferous component, the aforementioned metal oxides and salts of metals should be preferred.

For enhancing the stabilizing effect, cerium oxide, iron oxide or copper oxide are preferred as the metal oxides.

=For enhancing-the stabilizing effect, cerium naphthenate, lanthanum naphthenate or ytterbium naphthenate are preferred as the salts of metals.

The stabilizing additives are introduced as follows.

Polyorganosiloxanes belonging to those that contain aliphatic, aromatic, arylaliphatic and unsaturated radicals at the silicon atom and compositions based on such polyorganosiloxanes are mixed with stabilizing additives either in the dry state or in combined solutions or suspensions in organic solvents are prepared with subsequent removal of the latter.

At present it is an established fact that the ageing of polyorganosiloxanes proceeds in two ways, namely, there takes place oxidation of the organic portion of the macromolecule by the radical mechanism and 'depolymerization of the main-polymeric chain with the formation of 1ow--molecular organosilicone products.

' The latter process proceeds in accordance with the heterolyticmechanism from the hydroxyl endsof the Some of the said methods are alsodisadvantageous in that the stabilizing effect is lost in case a filler or other components of rubber mixtures are used.

The object of the present invention is to enhance the thermostability of polyorganosiloxanes and, composi-. tions based thereon.

polymeric chains and is initiated by the catalyst residues. The destructive processes thus taking place are accompanied by crosslinking and loss of elasticity of the polymer. v 1 j W The introducing'of polyethynylpyridines as a stabilizing additive makes it possible to reducethe rate of 3 oxidation processes up of temperatures close to 400C and preserve the elastic properties of polyorganosiloxanes when they are heated to said temperatures.

This is attained due to the fact that polyethynylpyridines inhibit oxidation processes and at the same time suppress the development of heterolytic processes. Polyethynylpyridines are preserved 'in the polymer without exhibiting any noticeable changes when the polymer is heated to high temperatures. Thus, for example, derivatographic analysis of poly-2-methyl-5- ethynyl-pyridine has shown its decomposition with the evolution of gaseous products to commence at a temperature of 328330C, with only l2-l4 weight percent of the total initial quantity to have escaped by 400C. Polyethynylpyridines are readily soluble in organic solvents and are compatible with polyorganosiloxanes.

The stabilizing effect of a polyethynylpyridine is enhanced when it is introduced as a stabilizing additive in a mixture with a metalliferous component.

Due to the introduction of polyethynylpyridines or a mixture of a polyethynylpyridine with a metalliferous component as stabilizing additives, the present method ensures an enhancement in the thermostability of polyorganosiloxanes, when ageing, up to 400C.

The stabilizing effect is not diminished in case a filler is introduced or when vulcanization is carried out.

For a better understanding of the present invention, given hereinbelow are examples illustrating the way in which the proposed method for increasing the thermostability polyorganosiloxanes can be realized.

EXAMPLE 1 100 parts by weight of polymethylvinylsiloxane rubber comprising vinyl units, prepared on a sulphuricacid catalyst and having a neutral character of the aqueous extract, are mixed on conventional mill rolls at room temperature with 1 part by weight of poly2- methyl--ethynylpyridine. This mixture is subjected to thermooxidation ageing at temperatures of 300 to 350C, records being made of the kinetics of weight losses and changes in the elastic properties of the samples with time. Similar specimens are heated at a constant rate of 3 deg/min with the temperature of the commencement of the specimen intensive decomposition being determined thermogravimetrically and the temperature interval of the exothermal peak which is responsible for the oxidation of the organic radicals being determined with the help of the differential thermal anaylsis method.

For comparison specimens of rubber without any additives and with an additive consisting of 5 parts by weight of Fe2O are tested under the same conditions.

The results are presented in Table 1.

EXAMPLE 2 100 parts by weight of rubber similar to that described in Example I are mixed on mill rolls with 40 parts by weight of a fine disperse silica filler (white soot) and 1 part. by weight of poly-Z-methyl-S-ethynylpyridine. The composition thus prepared is subjected to ageing at a temperature of 350C and also under heating at a constant rate of 3 deg/min. For comparison, under similar conditions a composition is prepared and tested which consists of rubber with 20 to 40 parts by weight of white soot as a filler and with 3 parts by weight of Fe 0 as an additive. The test results are presented in Table 3. v

EXAMPLE 3 I00 parts by weight of industrial polydimethylsiloxane rubber with a molecular weight of4.5. l 0 obtained on a sulphuric-acid catalyst and featuring neutral character of the aqueous extract are mixed on mill rolls with 3 parts by weight of poly-Z-methyl-S-ethynylpyridine. The tests are carried out under the conditions similar to those described in Example 1. The results are presented in Table 3.

EXAMPLE 4 parts by weight of rubber similar to that used in Example 3 are mixed with 1 part by weight of poly-2- methyl-S-ethynylpyridine and then 20 parts by weight of a fine disperse silica filler (white soot) are gradually introduced into the mixture so that it should be evenly distributed in the polymer mass in the course of milling. The resulting composition, after ageing in air at a temperature of 350C during 3 hours, loses 19% of its initial weight while preserving the elasticity. Weight losses in the reference specimen (without the use of the stabilizers recommended in the present invention) amount to 28%.

EXAMPLE 5 The process is carried out as described in Example 4, but poly-4-ethynylpyridine is introduced as a stabilizing additive. Weight losses after 3 hours of ageing in air at a temperature of 350C amount to 21%.

EXAMPLE 6 100 parts by weight of a polyorg-anosiloxanes elastomer containing methyl, phenyl and a sniall number of vinyl groups are mixed with 0.5 part by weight of poly 2-methyl-5-ethynylpyridine and 20 parts by weight of white soot. When heated in air at a temperature of 350C during 3 hours, the specimen loses 16% of its weight while preserving its rubber-like properties. The reference sample without the stabilizing additive under the same conditions loses 27% of its weight.

EXAMPLE 7 100 parts by weight of rubber similar to that used in Example 6 are mixed with 1 part by weight of poly-2- methyl-5-ethynyl-pyridine. When the test specimen is heated in air at a rate of 3 deg/min, its intensive decomposition commences at a temperature of 398C and the exothermal peak characterizing oxidation of organic radicals lies in the range of 390-403C. The reference specimen (without the stabilizer) starts decomposing at a temperature of 342C and the corresponding exothermal peak lies within the temperature range of 325-342C.

EXAMPLE 8 The process is carried out as described in Example 7, but i part by weight of poly-4-ethynylpyridine is introduced as a stabilizer. The intensive decomposition of this mixture, when heated in air at a rate of 3 deg/min, commences at a temperature of about 400C. The exothermal peak which characterizes the oxidation has shifted by 60 65C towards higher temperatures as compared with the non-stabilized specimen.

EXAMPLE Polyorganosiloxane rubber similar to that described in Example 1, but differing in that the terminal OH- groups of the polymeric chains are substituted by trimethoxysilyl ones, is mixed in benzene with 1 weight part of poly-2-methyl-5-ethynylpyridine. After the removal of the solvent under vacuum (r'arefaction of l0- mm Hg), the specimen is heated in air at a rate of 3 deg/min. The temperature of the commencement of its weight losses is 362C, by 400C the losses amounting only to 3% of the initial weight. The sample without the addition of poly-2-methyl-5-ethynylpyridine features the commencement of destruction at a temperature of 335C and by 400C the reference sample loses of its initial weight. The exothermal peak characterizing the oxidation of hydrocarbon radicals is shifted for the stabilized sample by more than 50C towards higher temperatures.

EXAMPLE 10 into the organo-silicon polymer described in the preceding Example there are introduced on mill rolls parts by weight of a filler (white soot) and 1 part by weight of poly-2-methyl-5ethynylpyridine per 100 parts by weight of the polysiloxane. The tests of the resulting mixture under non-isothermal heating conditions (3 deg/min) show the temperature of the commencement of intensive decorn'positionto be 383C and the exothermal peak of the oxidation of hydrocarbon radicals to lie within 3954l5C. The mixture filled with 20 parts by weight of white soot but containing no stabilizer starts decomposing at a temperature of 350C. The exothermal peak corresponding to the oxidation lies within the range of 342369C.

EXAMPLE 11 white soot and 5 weight parts of FeZO but containing no stabilizing additive, after being tested under the same conditions, loses 14.1% of its weight and becomes an easily crumbling mass devoid of elastic properties. A sample consisting of 100 parts by weight of rubber, 40 weight parts of the filler and 0.5 part by weight of poly- Z-methyl-S ethynylpyridine,though preserves its elastic properties, loses approximately twice as much in its' weight as the specimen stabilized with a mixture of poly-2-methyl-5-ethynylpyridine and iron oxide.

' A non-stabilized mixture consisting of 100 parts by weight of rubber and 40 parts by weight of white soot loses 24% of its weight and becomes a brittle vitreous mass.

EXAMPLE 1.2

The "process is carried out as described in Example 11, there being introduced a's a stab ilizer 3 parts by weight of poly-2-m ethyl-5-ethynylpyridme and 5 parts by weight of F6203. After the ageing the specimen loses 13.3% of its weight and preserves elasticity.

EXAMPLE 13 At room temperature on mill rolls thereare mixed 100 parts by weight of rubber similar to that described in Example 1 with 40 parts: by weight of white soot, 3 weight parts of cerium oxide and 0.5 part by weight of poly-2-methyl-5-ethynylpyridine. Theresulting mixture is subjected to ageing in air at a temperature of 350C during 3 hours. The test specimen loses 12.4% of its weight and remains soft and elastic. A sample of a rubber mixture consisting of parts by weight of rubber, 40 parts by weight of white soot and 3 parts by weight of CeO after being tested under the same conditions, loses about 13% of its weight, becomes covered with .a rigid film and easily crumples.

I EXAMPLE [4 EXAMPLE l5 On mill rolls a,mixture is prepared consisting of 100 parts by weight of rubber similar to that of Example 1, i

1 part by weightof poly-'2-m'ethyl-5-ethynylpyridine and 1 part by weight of ceriumnaphthenate. The mixture is heated inair under nonisothermal conditions. The temperature of the commencement of intensive decomposition is about 390C, the exothermal oxidation peak lies within 378408C. Tested under the same conditions is a specimen containing 100 parts by weight of rubber and 1 part by weight of cerium naphJ thenate. This specimen starts decomposing at a temper: ature of 340C and the exothermal peak that character izes oxidation lies within 346 -360C. 7

. EXAMPLE 16 The process is carriedout as described in Example 15. As a stabilizing'additivel part by weight of poly-2- methyl-5-ethynylpyridine and l part'by weight of ytterbium naphthenate are used. Being heated at .a rate of 3 deg/min, the stabilized specimen startsdecomposing at a temperature of 385C. A specimen consisting of 100 parts by weight of rubber and 1 part by weight of yt terbium naphthenate shows the commencement of .de-'" struction at a temperature of 333C and the corresponding'exothermal peak lies within 318-340C.

EXAMPLE l7 EXAMPLE 18 v The process is carried out as described in Example 15, with the use of gadolinium oxide as the metalliferous component of the stabilizing additive.

The results of the test when the sample is subjected to ageing under non is'othermal heating conditions are similar to those featured by the sample in Example 15.

7 The destruction of the specimen containing 100 parts by weight of rubber and 1 part by weight of'gadolinium naphthenate commences at a temperature of 342C and the exothermal peak lies within 321350C.

EXAMPLE 19 On mill rolls at room temperature there are mixed 100 parts by weight of rubber similar to that used in Example 1 with 50 parts by weight of white soot, 1 part by weight of poly-2-methyl-5-ethynylpyridine and 3 parts by weight of BaO as a metalliferous component. The resulting mixture is tested for resistance to thermooxidation ageing under the conditions of non-isothermal heating (3 deg/min), with records being made of the commencement of intensive decomposition and the range of the exothermal peak, the respective temperature values being found to be 255C and 365416C.

The results of testing a specimen consisting of 100 parts by weight of rubber, 50 parts by weight of white soot and 3 parts by weight of BaO show 280C and 352-375C respectively. When such a specimen is heated during 3.5 hours in air under isothermal conditions (350C), it is completely cross-linked and becomes a vitreous product. Under the same conditions the rubber mixture comprising the stabilizing composition remains elastic and soft.

EXAMPLE 20 The process is similar to that described in Example 19. 3 parts by weight of A1 are used as a metalliferous component of the stabilizing additive.

The specimen is tested for resistance to thermooxidation ageing under the conditions similar to those described in Example 19. For comparison, under the same conditions a specimen is subjected to ageing, which contains no poly-2-methyl-5-ethynylpyridine.

The tests have shown the stabilized rubber mixture to feature the commencement of intensive weight losses at a temperature of 365C and the exothermal peak to lie within 360408C. The respective values for the sample containing no poly-2-methyl-5-ethynylpyridine are 350C and 350379C.

For heating effected in air during 3.5 hours at a temperature of 350C, the weight losses are as follows.

For the stabilized specimen, 21%, the specimen remaining soft and elastic; for the specimen containing no poly-2-methyl-5-ethynylpyridine, 24%, the specimen becoming a vitreous mass.

EXAMPLE 2] The process is carried out as in Example 19. 3 parts by weight of CuO are used as a metalliferous component.

The tests performed under the conditions similar to those described in Example 19 have shown the decomposition to commence at 370C and the exothermal peak to lie within 360410C. The weight losses during 3.5 hours of ageing in air at 350C are 18%; the specimen preserves its elastic properties.

The results of concurrent testing of the specimen consisting of 100 parts by weight of rubber, 3 parts by weight of CuO and 50 parts by weight of white soot have shown the decomposition temperature thereof to be 350C, the exothermal peak to lie within 350379C and the weight losses at a temperature of 350C during 3.5 hours to be 26.5%. After ageing under isothermal conditions the specimen is brittle.

EXAMPLE 22 A rubber mixture is prepared on mill rolls, consisting of parts by weight of rubber similar to that used in Example 1, 50 parts by weight of white soot, 3 weight parts of poly-2-methyl-5-ethynylpyridine and 5 parts by weight of F e 0 The mixture is subjected to ageing in air during 6 hours at a temperature of 350C or during 36 hours at a temperature of 320C. After that the percent of equilibrium swelling in toluene at a temperature of 25C and the content of the sol-fraction (solubility) are determined. The results are presented in Table 4. For comparison tabulated in the same Table are the results of testing the specimens which either contain no stabilizing additive or contain only one of the components of such additive.

EXAMPLE 23 Prepared on mill rolls are rubber mixtures based on rubber similar to that used in Example 1, these mixtures containing as a filler an aerogel SiO (hydrophobized aerosil) and as a stabilizing additive 3 parts by weight of poly-2-methyl-5-ethynylpyridine and 5 parts by weight of Fe O The conditions and results of the tests are presented in Table 5.

EXAMPLE 24 Prepared on mill rolls is a rubber mixture based on a poly-methylvinylsiloxane rubber differing from that described in Example 1 by the content of vinyl groups, said mixture containing 100 parts by weight of the rubber, 50 parts by weight of white soot, 5 parts by weight of FezO 0.25 part by weight of poly-2-methyl- S-ethynylpyridine and 0.3 part by weight of dicumyl peroxide. After press vulcanization (C, 20 min, 75 kg/cm and thermostating in air (200C, 6 hours),

specimens (plates 0.5 mm thick and plugs 4 mm in diameter) are subjected to thermooxidation ageing.

After 6, 12, 24 and 60 hours at a temperature of 250C and 1-4 hours at a temperature of 300C the overstrain accumulation in the plugs is determined, and after ageing at temperatures of 320 and 350C conditional equilibrium modulus is determined for the plugs and plates. The results of the tests are presented in Tables 6 and 7.

EXAMPLE 25 The process is carried out as described in Example 24, the difference being in that 0.5 part by weight of poly-2-methyl-5-ethynylpyridine is introduced into the rubber mixture prior to the vulcanization. The results of the tests are given in Tables 6 and 7.

EXAMPLE 26 The process is carried out as described in Example 24, the difference being in that 1 part by weight of poly-2-methyl-5-ethynylpyridine is introduced into the rubber mixture. The results of the tests are presented in Tables 6 and 7.

EXAMPLE 27 The process is similar to that described in Example 24, the only difference being in that 2 parts by weight of poly-2-methyl-5-ethynylpyridine are introduced into the rubber mixture. The results of the tests are presented in Tables 6 and 7.

EXAMPLE 28 I The process is carried out as described in Example EXAMPLE 29 that comprises 100 parts by weight of the polysiloxane, 35 parts by weight of silica as a filler, parts by weight of iron oxide, 0.25 part by weight of poly 2-methyl-5 after which the conditional equilibrium modulus is determined The results are presented-in. Table 8 in which, data are also given pertaining to the testing of a specimen containing only Fe O as the stabilizer.

EXAMPLE The process is c arried oufas described in Example 29, the only difference being'in that 0.5 part by weight On the basis of rubber similar to that described in 1 of poly'z'methylns'ethynylpyridine is introduced into Example 24 a rubber mixture is prepared-on mill rolls therubber mixture The results of the tests are presented in Table 8.

EXAMPLE 3i The process is carried out as described in Example Table 1 Heating under isothermal conditions Temperature range of exothermal Heating at peak that 1 Character- 21 rate of characterizes istics 3 deg/min oxidation Weight of specimen Temperature of of organic losses after commencement radicals Weight at testing of intensive ofpol'ylosses 350C under weight organosiloxat during isothermal Nos. Specimen losses. "C anes. C 300C 3 hrs. 71 conditions 1. Polymethylvinylsilof xane rubber lcom rising during vitreous.

viny units 320 305-325 l0 hrs 34 brittle 2. Polymethylvinylsiloxane'rubber comprising I vinylu'nits, I00 weight parts; poly- 2-methyl-5- ethynylpyridine, 24% 1 weight during elastic. part i 380 370378 hrs 15 soft 3. Polymethyl- ,ili' ir y oxane rubber com rising viny units. weight parts;Fe,O 24% 5 weight i during vitreous, parts 365 350-365 80 hrs 30 brittle Table 2- Isothermal heating Temperature range of Heating at exothermal a rate of peak that 3 deg/min characterizes Temperature of oxidation Weight Characteristics commencement of organic losses of specimen of intensive radicals of at 350C after weight polyorganoduring isothermal Nos. Specimen losses, C siloxane. "C 3hrs;% oxidation 1. Polymethylvinylsiloxane rubber, l00 wt.pt.; white soot, 20 wt.pt. 355 352-368 23.0 brittle 2. Polymethylvinylsilo- Table 2;continued Isothermal heating Temperature range of Heating at exothermal .a rate of peak that 3 deg/min characterizes Temperature of oxidation Weight Characteristics commencement of organic losses of specimen of intensive radicals of at 350C after weight polyorgano- I during isothermal Nos. Specimen losses. C siloxane. C 3 hrs. 7c oxidation xane rubber. I00 wt.pt.; white soot. 4O wt.pt. 372' 360-390 23.8 i brittle 3. Polymethylvinylsiloxanerubber. it. I00 wt.pt.; 7 white soot, l 20 wt.pt.; poly-Z-methyl- 5; S-ethynylpyridine. elastic. l wt.pt. 400 390-420 17.0 soft 4. Polymethylvinylsiloxane rubber. I00 wt.pt.; white soot. 20 wt.pt.; F5203 3 wt.pt. 373 I 370-380 2L6 crumpling Table 3 Temperature range of Heating at exothermal a rate of peak that 3 deg/min characterizes Temperature of oxidation Weight Characteristics commencement of organic losses ofspecimen of intensive radicals of at 350C after weight polyorganoduring isothermal Nos. Specimen losses. C siloxane. "C 3 hrs. 7:- oxidation l. Polydimethylv siloxane rubvitreous, ber 327 295-335 36.0 r brittle 2. Polydimethylsiloxane rubber. 100 wt. pt.; poly-2- methyl-S-ethynylpyridielastic. ne.3 wt. pt. 373 365-376 25 soft Table 4 350C. 6 hours 320C. 36 hours Equilibt i t Solubi-. rium Equilibrium Nos. Rubber mixture lity. swelling. 7? swelling,

l. Non-stabilized I77 2. Containing 5 wt...pt. of F O 2.8 219 310 3. Containing 3 wt. pt. of poly-Z-methyl- S-ethynyIpyridine 4.6 216 212 4. Containing 3 wt. pt. of

poly-Z-methyl- S-ethynylpyridine and 5 wt. pt. Of F6203 11.1 327 3'36 13 14 Table 5 5. A method for increasing the thermostability of organopolysiloxane elastomers according to claim 1, Wet ht arts Components g p further comprising mixing m about I to 10 parts by f jg 'gf 100 100 100 weight of a metal salt selected from the group consistl-lydrophobized aerosil 50 50 50 50 ing of cerium naphthenate, lanthanum naphthenate, poll'gTmethymethyny" 3 3 and ytterbium naphthenate per 100 parts by weight of 32 0; 5 5 said organopolysiloxane.

6 A method for increasing the thermostability of solublmyfln tiiilfigi 14.8 1.9 24 10 organopolysiloxane elastomers accord ng to claim 1, 350C further comprising mixing in a reinforcing filler, a cur- 6 hours ing agent, and l to 10 parts by weight of a salt of a Equilibrium Vitreous metal selected from the group consisting of cerium Swenmgg Pwde' 386 538 naphthenate, lanthanum naphthenate, and ytterbium Table 6 Values of Conditional Equilibrium Modulus of Rubbers after Ageing, kg/cm Plates Plugs Amount, 320C 320C sso c 320C soo' 'c 320C 350C 350C Nos. Stabilizer wt. pt. lday Zdays Shrs Bdays l2days 36hrs Shrs lOhrs l. Fe O 5 I45 300 370 245 400 I25 430 2. Poly -2-me P y 7 ethynyl pyridine Fe O 0.25/5 I I 330 3. 0.5/5 95 I 325 250 4. H5 95 I 380 300 5. 2/5 110 205 6. 3/5 270 I 155 Table 7 Compression Overstrain Accumulation in Rubbers after Ageing Amount, 250C 300C Nos. Stabilizer wt. pt. 6 hrs l2 hrs 24 hrs 60 hrs 1 hr 2 hrs 4 hrs 1 1. mo. 5 0.18 0.26 0.30 0.5l 0.26 0.4! 0.79 2. Poly-2 -methyl- S -ethynyISyridine an F820;, 0.25/5 0.20 0.27 0.29 0.40 0.23 0.29 0.48 3. 0.5/5 0.17 0.22 0.25 0.36 0.22 0.29 0.45 4. 1/5 0.23 0.30 0.34 0.49 0.30 0.39 ().5l 5. 2/5 0.26 0.32 0.41 0.59 0.38 0.48 0.62

Table 8 Values of Conditional Equilibrium Modulus of Rubbers after Ageing. k lcm Nos. Stabilizer Amount, wt. pt. 3 0C.8 days 320C.36 hrs 1. Fe o 5 115 600 2. Poly-Z-methyl- S-ethynylpyndine and Fe O 0.25/5 I35 640 3. 0.5/5 I34 4. H5 I16 2. A method for increasing the thermostability of 60 organopolysiloxane elastomers according to claim 1, wherein said polyethynylpyridine is selected from the group consisting of poly-2-methyl-5-ethynylpyridine, poly-2-ethynylpyridine, and poly-4-ethynylpyridine.

3. A method for increasing the thermostability of 65 organopolysiloxane elastomers according to claim 2, further comprising mixing in a reinforcing filler.

4. A method for increasing the thermostability of organopolysiloxane elastomers compositions according to claim 3, further comprising mixing'in a curing agent, and curing the composition obtained.

naphthenate, and curing the composition thus obtained.

7. A method for increasing the thermostability of 55 organopolysiloxane elastomers according to claim 1,

further comprising mixing in l to 10 parts by weight of a metal oxide selected fromrthe' group comprising copper oxide, barium oxide, aluminum oxide, cerium oxide, gadolinium oxide and iron oxide.

8. A method for increasing 'rthe thermostability of organopolysiloxane elastomers compositions according to claim 7, further comprising mixing in a reinforcing filler, and a curing agent, and curing the composition thus obtained.

9. A method for increasing the thermostability of organopolysiloxanes according to claim 1, wherein said organopolysiloxane is selected from the group consisting of polymethylvinylsiloxane, polydimethylsiloxane, polymethylphenylsiloxane, and polymethylvinylsiloxane having terminal trimethoxysilyl groups. 

1. A METHOD FOR INCREASING THE THERMOSTABILITY OF ORGANOPOLYSILOXANE ELASTOMERS CONTAINING ALIPHATIC, AROMATIC, ARYLALIPHATIC OR UNSATURATED RADICALS AT THE SILICON ATOM COMPRISING MIXING TOGETHER SAID ORGANOPOLYSILOXANE AND ABOUT 0.01 TO 10 PARTS BY WEIGHT OF A POLYETHYNYLPYRIDINE PER 100 PARTS BY WEIGHT OF ORGANOPOLYSILOXANE.
 2. A method for increasing the thermostability of organopolysiloxane elastomers according to claim 1, wherein said polyethynylpyridine is selected from the group consisting of poly-2-methyl-5-ethynylpyridine, poly-2-ethynylpyridine, and poly-4-ethynylpyridine.
 3. A method for increasing the thermostability of organopolysiloxane elastomers according to claim 2, further comprising mixing in a reinforcing filler.
 4. A method for increasing the thermostability of organopolysiloxane elastomers compositions according to claim 3, further comprising mixing in a curing agent, and curing the composition obtained.
 5. A method for increasing the thermostability of organopolysiloxane elastomers according to claim 1, further comprising mixing in about 1 to 10 parts by weight of a metal salt selected from the group consisting of cerium naphthenate, lanthanum naphthenate, and ytterbium naphthenate per 100 parts by weight of said organopolysiloxane.
 6. A method for increasing the thermostability of organopolysiloxane elastomers according to claim 1, further comprising mixing in a reinforcing filler, a curing agent, and 1 to 10 parts by weight of a salt of a metal selected from the group consisting of cerium naphthenate, lanthanum naphthenate, and ytterbium naphthenate, and curing the composition thus obtained.
 7. A method for increasing the thermostability of organopolysiloxane elastomers according to claim 1, further comprising mixing in 1 to 10 parts by weight of a metal oxide selected from the group comprising copper oxide, barium oxide, aluminum oxide, cerium oxide, gadolinium oxide and iron oxide.
 8. A method for increasing the thermostability of organopolysiloxane elastomers compositions according to claim 7, further comprising mixing in a reinforcing filler, and a curing agent, and curing the composition thus obtained.
 9. A method for increasing the thermostability of organopolysiloxanes according to claim 1, wherein said organopolysiloxane is selected from the group consisting of polymethylvinylsiloxane, polydimethylsiloxane, polymethylphenylsiloxane, and polymethylvinylsiloxane having terminal trimethoxysilyl groups. 